Leadframe With Vertically Spaced Die Attach Pads

ABSTRACT

A leadframe includes a first die attach pad (“DAP”) having a first longitudinally extending edge surface and a second DAP having a first longitudinally extending edge surface. The second DAP is positioned with the first longitudinally extending edge surface thereof in adjacent, laterally and vertically spaced relationship with the first longitudinally extending edge surface of the first DAP.

This application is a Divisional of application Ser. No. 15/151,177filed May 10, 2016.

BACKGROUND

Some integrated circuit (“IC”) packages require isolation between apower source and a monitor or control circuit. Such IC packages mayemploy a leadframe with split die attach pads to ensure isolation of therespective grounds.

SUMMARY

A leadframe includes a first die attach pad (“DAP”) having a firstlongitudinally extending edge surface and a second DAP having a firstlongitudinally extending edge surface. The second DAP is positioned withthe first longitudinally extending edge surface thereof in adjacent,laterally and vertically spaced relationship with the firstlongitudinally extending edge surface of the first DAP.

A leadframe assembly includes a first die attach pad (“DAP”) having afirst longitudinally extending edge surface and a second DAP having afirst longitudinally extending edge surface. The second DAP ispositioned with the first longitudinally extending edge surface thereofin adjacent, laterally and vertically spaced relationship with the firstlongitudinally extending edge surface of the first DAP. A first die ismounted on the first DAP and a second die is mounted on the second DAP.

An integrated circuit package includes a leadframe assembly with a firstdie attach pad (“DAP”) having a first longitudinally extending edgesurface and a second DAP having a first longitudinally extending edgesurface. The second DAP is positioned with the first longitudinallyextending edge surface thereof in adjacent, laterally and verticallyspaced relationship with the first longitudinally extending edge surfaceof the first DAP. A first die is mounted on the first DAP and a seconddie is mounted on the second DAP. A layer of mold compound covers theleadframe and the first and second dies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top isometric view of a prior art leadframe with a first andsecond die attach pad (DAP).

FIG. 2 is a bottom isometric view of the prior art leadframe of FIG. 1.

FIG. 3 is a top isometric view of a leadframe with two DAPs that arepositioned at different elevations.

FIG. 4 is a bottom isometric view of the leadframe a FIG. 3.

FIG. 5 is a partially cutaway, top plan view of an integrated circuitpackage having the leadframe illustrated in FIGS. 3 and 4.

FIG. 6 a schematic view of the two DAPs of FIGS. 1 and 2 with attacheddies.

FIG. 7 is a schematic view of the two DAPs of FIGS. 3 and 4 withattached dies.

FIG. 8 illustrates a method of redesigning an integrated circuit packagewithout changing the package footprint.

DETAILED DESCRIPTION

As used in this disclosure, directional terms such up, down, above,below, top, bottom, vertical, lateral, horizontal, etc., are used in arelative sense to establish a frame of reference for describing therelationship between objects or parts of objects, usually with referenceto the drawings. These terms are not used in any absolute sense, such aswith reference to the surface of the earth. Thus, as used in thisrelative sense, the writing surface of a desk, once referenced as thetop of the desk, would still be correctly referred to as the top of thedesk, even if the desk were flipped onto one side or upside down.

FIG. 1 is a top isometric view of a prior art leadframe 10 and FIG. 2 isa bottom isometric view of the prior art leadframe of FIG. 1. Theleadframe 10 has a first die attach pad (“DAP”) 11 and second DAP 41.The first DAP 11 has a top surface 12, a bottom surface 13, and a firstvertical edge 14 extends between the top and bottom surfaces. A firsttie bar 16 and a second tie bar 18 support the first DAP 11 within theleadframe 10 and connect the DAP 11 to a first dam bar 32. The first DAP11 is surrounded on one side by a first plurality of leads 20 thatincludes a first lead 24, second lead 26, a third lead 28, etc. Outerend portions of the first plurality of leads 20 are connected to thefirst dam bar 32. The first dam bar 32 is in turn connected at one endto a first support rail 34 and at a second end to a second support rail36.

The second DAP 41 has a top surface 42, a bottom surface 43 and avertical edge service 44. The second DAP 41 is connected to theleadframe 10 by a first tie bar 46 and the second tie bar 48. The tiebars 46, 48 support the DAP 41 within the leadframe 10. A plurality ofleads 50, including a first lead 52, a second lead 54, third lead 56,etc., are positioned around one side of the second DAP 41. Outerportions of the tie bars 46, 48 and the plurality of leads 50 areconnected to a second dam bar 62. The second dam bar 62, like the firstdam bar 32, is connected at opposite ends to the first and secondsupport rails 34, 36.

The first vertical edge surface 14 of the first DAP 11 and the firstvertical edge surface 44 of the second DAP 41 are parallel surfaces thatare positioned in opposed adjacent relationship and separated by a gap70.

FIG. 6 a schematic view of the two DAPs 11, 41 of FIGS. 1 and 2 withattached dies 72, 74. The leadframe 10, DAPs 11, 41 and dies 72, 74mounted thereon are covered with a layer of mold compound (not shown)that ordinarily fills the gap 70 between the two DAPs 11,41. Theseparation distance “x” between the two dies is sufficient to prevent apartial dielectric discharge failure (“PD failure”) when the gap 70 isfilled with mold compound. However, during the molding process, bubblessometimes form in the mold compound such that the gap 70 is not entirelyfilled with mold. The gap 70 may then be filled partially or entirelywith air. Because the dielectric coefficient of air is less than that ofmold compound, a PD failure may occur when there is an air void in thegap 70 and the separation distance between DAPs 11, 41 is only x.

FIG. 3 is a top isometric view of a leadframe 110 with two DAPs 111, 141that are positioned at different elevations. FIG. 4 is a bottomisometric view of the leadframe 110 of FIG. 3. The first leadframe 110has a first DAP 111 having a top surface 112, a bottom surface 113 and afirst edge surface 114 extending therebetween. A first tie bar 116connects one end of the first DAP 111 to a first dam bar 132. The firsttie bar 116 has a down-set portion 117. A second tie bar 118 connectsthe other end of the first DAP 111 to the first dam bar 132. The secondtie bar 118 has a down-set portion 119. The tie bars 116, 118 anddown-set portions 117, 119 thereof are constructed and arranged suchthat the top surface 112 of the DAP 111 is positioned in parallelrelationship to the top surface of the first dam bar 132, but at a lowerelevation. The first DAP 111 is surrounded on one side by a plurality ofleads 120 that are positioned at an elevation above that of the firstDAP 111. The leads 120 may include a first lead 122, a second lead 124,etc.

With continued reference to FIGS. 3 and 4, the leadframe 110 has asecond DAP 141 with a top surface 142, bottom surface 143 connected byan edge surface 144. The leadframe 110 has a first DAP 111 having a topsurface 112, a bottom surface 113 and a first edge surface 114 extendingtherebetween. A first tie bar 146 connects one end of the second DAP 141to a second dam bar 162. A second tie bar 148 connects the other end ofthe second DAP 141 to the second dam bar 132. The second DAP 141 issurrounded on one side by a plurality of leads 150 that are positionedat an elevation above that of the first DAP 111. The leads 150 mayinclude a first lead 152, a second lead 154, etc. The second DAP 141 ispositioned parallel to and at a higher elevation than the first DAP 111.The two opposite vertical edge surfaces 114, 144 of the two DAPs 111,141 are parallel surfaces but at different horizontal levels, asdescribed further below.

FIG. 5 is a top plan view of an integrated circuit (IC) package 168 thatincorporates the leadframe 110 illustrated in FIGS. 3 and 4. The ICpackage 168 includes a first die 172 mounted on the first DAP 111, and asecond die 174 mounted on the second DAP 141. The two dies 172, 174 areelectrically connected by one or more bond wires 176. The first die 172is also connected by bond wires 180 to at least some of the leads 120.The second die 174 is electrically connected to at least some of theleads 150 by bond wires 182. A layer of mold compound 190, only a smallfragment of which is shown in FIG. 5, covers the entire leadframe 110,dies 172, 174 and bond wires 176, 180, 182. In some IC packageembodiments outer end portions of the leads on 120, 150 are exposed atsurface portions of the mold compound layer 190.

The leadframe 110, shown in FIGS. 3 and 4, is a modified design of theleadframe shown in FIGS. 1 and 2. This design eliminates problem ofpartial electrical discharge due to the presence of air in the gap 70between the two DAP edge surfaces 14, 44 in the old design. With thisnew design, it is not necessary to increase the lateral distance betweenthe adjacent DAP edge surfaces (i.e., 14, 44 in the old design and 114,144 in the new design both have the same lateral spacing “x”). Also itis not necessary to move the two dies mounted on the DAPs farther apart,which would require the use of laterally larger DAPs or smaller dies, ifthe lateral spacing x between the DAPs were to remain unchanged. Thus,the foot print of the redesigned leadframe 110 may remain the same asthe footprint of the original leadframe 10 and the size of the dies usedmay remain the same. This is a significant manufacturing advantagebecause most of the manufacturing tooling and packaging can remainunchanged. Expensive replacement operations are thus avoided.

The difference between the two leadframes 10, 110 are illustrated byFIGS. 6 and 7. In the original leadframe 10, as shown schematically inFIG. 6, the distance between the two vertical edge surfaces 14, 44necessary to avoid partial discharge failure with mold compound fillinggap 70 is distance Y. However, as shown schematically by FIG. 7, theseparation distance between the two edge surfaces to prevent partialdischarge failure when there is only air in gap 70, is a larger distance“Y” (not shown). If this larger distance were achieved by moving the twoDAPs 11, 41 farther apart laterally, it would change the footprint ofthe leadframe 10, which is undesirable. If this larger separationdistance were achieved by using smaller DAPs it would also requiresmaller versions of dies 72, 74, in order to fit them on the smallerDAPs, another undesirable change.

However, in the redesigned leadframe 110, schematically illustrated inFIG. 7, the effective separation distance between the edge surfaces 114and 144 of DAPs has been changed to “z”, which is greater than x, bychanging the relative elevations of the two DAPs, for example, bylowering DAP 111 relative to DAP 141. The effective separation distancehas also been increased by changing the slope of the two edge surfaces114 and 144 so that they are no longer two planar parallel surfaces. Inthe illustrated embodiment the shape of the edge surfaces 114 and 144have been changed by sloping each surface 114 and 144 downwardly andaway from the other surface. Generally, the greater the slope, thelarger the effective distance Z becomes. In another embodiment, shown bydashed lines in FIG. 7, the two surfaces 114 and 144 have been rounded,which also has the effect of increasing the effective separationdistance z between surfaces 114 and 144, as compared to the originalparallel edge surfaces 14, 44.

It will be understood by those skilled in the art that relativeelevation differences can be achieved by raising or lowering either DAPrelative the other or by raising one while lowering the other. It doesnot matter which of the DAPs is at the relatively higher elevation.

It will be appreciated from the above that method of redesigning anintegrated circuit package without changing the package footprint hasbeen disclosed herein. The integrated circuit package is of the typehaving a leadframe assembly with a first and second die attach pad(“DAP”) each having a top surface and a vertical edge surface, the topsurfaces positioned at the same elevation, the vertical edge surfacesbeing parallel and separated by a gap having a gap distance, saidintegrated circuit package being subject to partial electrical dischargefailure associated with air in mold compound that ordinarily fills thelateral gap. The method is illustrated in FIG. 8 and includes, as showna block 201, lowering the first DAP top surface relative to the secondDAP top surface while maintaining the lateral gap distance unchanged.The method may further include changing at least one of the verticaledge surfaces to a non-vertical edge surface.

Embodiments of a leadframe with die attach pads at different elevationsand various assemblies and IC packages that incorporate this leadframehave been expressly described in detail herein. Various alternativeleadframe embodiments, leadframe assembly embodiments and IC packageembodiments, will occur to others skilled in the art after reading thisdisclosure. It is intended that the language of the appended claims beconstrued broadly to cover all such alternative embodiments, except aslimited by the prior art.

1. A leadframe comprising: a first die attach pad (“DAP”) having a firstlongitudinally extending edge surface; and a second DAP having a firstlongitudinally extending edge surface, said second DAP being positionedwith said first longitudinally extending edge surface thereof inadjacent, laterally and vertically spaced relationship with said firstlongitudinally extending edge surface of said first DAP.
 2. Theleadframe of claim 1 wherein said first longitudinally extending edgesurface of said second DAP is positioned in nonparallel relationshipwith said first longitudinally extending edge surface of said first DAP.3. The leadframe of claim 2 wherein said first edge surface of saidfirst DAP slopes downwardly and laterally away from said second DAP. 4.The leadframe of claim 3 wherein said first edge surface of said secondDAP slopes downwardly and laterally away from said first DAP.
 5. Theleadframe of claim 2 wherein at least one of said first edge surfaces isa non-planar edge surface.
 6. The leadframe of claim 1 furthercomprising at least one downset tie-bar supporting said first DAP. 7.The leadframe of claim 6 wherein said at least one downset tie-barcomprises first and second downset tie-bars.
 8. The leadframe of claim 1further comprising a first set of leads positioned adjacent to saidfirst DAP and a second set of lead positioned adjacent to said secondDAP.
 9. The leadframe of claim 8 wherein said first DAP has a topsurface positioned at a first elevation and said second DAP has a topsurface positioned at a second elevation above said first elevation. 10.The leadframe of claim 9 wherein said first set of leads and said secondset of leads are positioned at said second elevation.
 11. A leadframeassembly comprising: a first die attach pad (“DAP”) having a firstlongitudinally extending edge surface; a second DAP having a firstlongitudinally extending edge surface, said second DAP being positionedwith said first longitudinally extending edge surface thereof inadjacent, laterally and vertically spaced relationship with said firstlongitudinally extending edge surface of said first DAP; a first diemounted on said first DAP; and a second die mounted on said second DAP.12. The leadframe of claim 11 wherein said first longitudinallyextending edge surface of said second DAP is positioned in nonparallelrelationship with said first longitudinally extending edge surface ofsaid first DAP.
 13. The leadframe assembly of claim 11 furthercomprising at least one downset tie-bar supporting said first DAP. 14.The leadframe assembly of claim 13 further comprising at least one bondwire having a first end electrically connected to said first die and asecond end electrically connected to said second die.
 15. The leadframeassembly of claim 11 further comprising a first set of leads positionedadjacent to said first DAP and a second set of leads positioned adjacentto said second DAP.
 16. The leadframe assembly of claim 11 wherein saidfirst DAP has a top surface positioned at a first elevation and saidsecond DAP has a top surface positioned at a second elevation above saidfirst elevation.
 17. The leadframe assembly of claim 12 wherein saidfirst set of leads and said second set of leads are positioned at saidsecond elevation.
 18. An integrated circuit package comprising: aleadframe assembly having: a first die attach pad (“DAP”) having a firstlongitudinally extending edge surface; a second DAP having a firstlongitudinally extending edge surface, said second DAP being positionedwith said first longitudinally extending edge surface thereof inadjacent, laterally and vertically spaced relationship with firstlongitudinally extending edge surface of said first DAP; a first diemounted on said first DAP; and a second die mounted on said second DAP;and a layer of mold compound covering said leadframe and said first andsecond dies. 19-20. (canceled)
 21. The integrated circuit package ofclaim 18 wherein said first longitudinally extending edge surface ofsaid second DAP is positioned in nonparallel relationship with saidfirst longitudinally extending edge surface of said first DAP.
 22. Theintegrated circuit package of claim 21 further comprising at least onedownset tie-bar supporting said first DAP.
 23. The integrated circuitpackage of claim 22 further comprising at least one bond wire having afirst end electrically connected to said first die and a second endelectrically connected to said second die.
 24. The integrated circuitpackage of claim 21 further comprising a first set of leads positionedadjacent to said first DAP and a second set of leads positioned adjacentto said second DAP.
 25. The integrated circuit package of claim 21wherein said first DAP has a top surface positioned at a first elevationand said second DAP has a top surface positioned at a second elevationabove said first elevation.
 26. The integrated circuit package of claim22 wherein said first set of leads and said second set of leads arepositioned at said second elevation.
 27. The integrated circuit packageof claim 21 wherein said first edge surface of said first DAP slopesdownwardly and laterally away from said second DAP.
 28. The integratedcircuit package of claim 27 wherein said first edge surface of saidsecond DAP slopes downwardly and laterally away from said first DAP. 29.The integrated circuit package of claim 21 wherein at least one of saidfirst edge surfaces is a non-planar edge surface.
 30. The integratedcircuit package of claim 13 wherein said at least one downset tie-barcomprises first and second downset tie-bars.